The invention relates to an electric lamp arrangement comprising:
a lamp cap provided with contacts; PA1 a rotationally symmetrical reflector provided with an axis of symmetry and a largest diameter d in a plane P transverse to the axis of symmetry; PA1 a first internally concave, mirroring wall portion behind the plane P which, in axial cross-sections at a first side of the axis is curved substantially according to a circular arc having a center of curvature in front of the plane P, which first wall portion is situated adjacent the lamp cap; PA1 a second internally concave, mirroring wall portion in front of the plane P which in axial cross-sections at the first side of the axis is substantially curved according to a circular arc having a center of curvature behind the plane P, at the other side of the axis; PA1 a light-transmissive window which is intersected by the axis; and PA1 an electric light source being arranged in the reflector in the vicinity of the axis and of the plane P and connected to current conductors which extend to the contacts of the lamp cap. PA1 the first mirroring wall portion in every axial cross-section at the first side of the axis is curved substantially according to a circular arc having its center of curvature situated in a region which lies predominantly at the other side of the axis and which is bounded by lines which enclose an angle .beta. and an angle .gamma. of 23.degree. and 39.degree., respectively, with the plane P and which intersect the plane P in the point where the first mirroring wall portion intersects the plane P at the first side of the axis; PA1 the second mirroring wall portion has a center of curvature which is situated in a region having the shape of an ellipse Q whose major axis has a first end in the plane P at a distance of 0.02 d from the axis of symmetry and a second end at a distance of 0.07 d from the plane P and 0.13 d from the axis of symmetry, which ellipse has a major axis which is 6.8 times the length of the minor axis; PA1 the light-transmissive window has a largest diameter smaller than 0.8 d. PA1 a second section near the plane P curved substantially according to a circular arc whose center of curvature is situated in a region one side of the axis and which has the shape of an ellipse T whose major axis has a first end at a distance of 0.32 d from the plane P and 0.10 d from the axis of symmetry and a second end at a distance of 0.49 d from the plane P and 0.33 d from the axis of symmetry, the major axis of this ellipse being 11.3 times the length of the minor axis. In this case the light beam has a higher luminous flux at acute angles to the axis than along the axis. The luminous flux is substantially proportional to cos.alpha..sup.-3 at an angle .alpha. to the axis of symmetry up to comparatively great angles, particularly when the centers of curvature of the first mirroring wall portion lie in a region having the shape of an ellipse S' uniform to and situated within the ellipse S with a point of intersection of its axes situated at 0.3 d away from the plane P and at 0.02 d from the axis of symmetry, at the other side thereof, and in a region having the shape of an ellipse T' uniform to and situated within the ellipse T with a point of intersection of its axes situated at 0.41 d away from the plane P and at 0.2 d from the axis of symmetry at the other side thereof, and when the second mirroring wall portion has a center of curvature situated in a region having the shape of an ellipse Q' uniform to and situated within the ellipse Q with a point of intersection of its axes situated at 0.03 d away from the plane P and at 0.06 d from the axis of symmetry.
The invention also relates to a blown bulb and to a reflector for use therein.
An electric incandescent lamp in which the reflector of the geometry described is integral with the lamp vessel of the incandescent lamp so as to form a reflector lamp is known from EP 0 284 117 B1.
A light source, an incandescent body, is arranged so as to surround the axis of the lamp vessel in this incandescent lamp. The mirroring wall portions form a light beam with a very high intensity in its center, along the axis. The beam has a small width of approximately 25.degree..
The small beam width of the known lamp is also apparent from the beam pattern depicted in FIGS. 2 to 5 of the cited Patent. It is clear from these Figures that the second mirroring wall portion must not extend to a greater distance away from the plane of largest diameter since this wall portion would then block out light coming from the first mirroring wall portion. As a result, the transmissive window is comparatively large and has a diameter which is more than 85% of the largest diameter; for lamps having a largest diameter of 60 mm, at least 86%; for lamps having a largest diameter of 95 mm, 89%.
The known lamp is suitable for brightly illuminating objects or areas of restricted dimensions; and thus for giving local light accents.
For other applications, however, it is desirable to have available a lamp which projects a comparatively wide beam and is thus capable of irradiating, for example lighting, a comparatively large field or large object. For alternative applications it is again necessary to irradiate a large field with a lamp emitting UV light, or IR light, for example, in stock breeding or for therapeutic purposes. It is true that for therapeutic applications the area to be irradiated is not extensive, but a small distance to the source of radiation is required for obtaining a high irradiation intensity, and therefore a comparatively wide beam.
It is noted that several types of reflector lamps, i.e. lamps having a mirroring coating on a portion of the lamp vessel, are available which give a wide light beam. The mirroring portion of the lamp vessel in these lamps is, for example, curved parabolically or elliptically, and the light-transmissive window is light-scattering, as is the surface of the portion on which the mirror is provided. The incandescent body in these lamps is outside the optical center. These lamps have their light-transmissive windows in the plane of largest diameter. They do not concentrate the generated light in a very effective manner and give much scattered light.